Interposers provide an electrical interface between two electronic assemblies, such as printed circuit boards. By providing an array of conductive members that couple to conductive pads on both electronic assemblies, the interposer can provide conductive paths carrying signals from one electronic assembly to another. In test systems, interposers can provide a separable interconnect between a device interface board, to which the devices under test (DUTs) are connected, and a tester interface board to which instruments that generate or measure test signals may be coupled.
Components of a test system are shown in FIG. 1. The test system 1 has an interposer 2, tester interface board 3, device interface board 4, DUTs 5, and instruments 6. In a test system, instruments 6 and tester interface board 3 are held within a test head, which is not shown for simplicity. Instruments 6 may be directly coupled to device interface board 4 through electrical connectors or may be coupled through cables or wires. Regardless, test signals generated or measured by instruments 6 are coupled through tester interface board 3.
Device interface board 4 may be mechanically coupled to a device handler or other apparatus that presents DUTs 5 for testing. For simplicity, the device handler also is not shown. In operation, DUTs 5 electrically connect to device interface board 4, allowing test signals to be coupled to or from DUTs 5 through device interface board 4.
Interposer 2 completes connections between device interface board 4 and tester interface board 3, allowing test signals to be coupled between instruments 6 and DUTs 5. To complete this coupling, interposer 2 makes connections between conductive pads on the lower surface of tester interface board 3 and conductive pads on the upper surface of device interface board 4.
Various mechanisms have been used to provide good electrical contact at both interfaces. These include spring contacts, dendritic contacts, “fuzz buttons”, elastomeric contacts, and direct contact. The connectivity of the contacts may be enhanced by an applying a force that presses tester interface board 3 towards device interface board 4.
An interposer typically has multiple conductive contacts, forming connections from one board to the other and allowing numerous test signals to be applied to or measured on the DUTs 5. In some test systems, the integrity of signals passing through an interposer is improved by grounding some of the conductive contacts. In some instances, a grounding pattern is used in which, for each conductive contact used to carry a signal, multiple conductive contacts adjacent to that signal contact are grounded.